Expandable interbody spinal fusion implant with expansion constraining member and method for use thereof

ABSTRACT

An implant cap is disclosed for preventing the over-expansion of an expandable spinal implant and method for use therewith. An implant cap also is disclosed for moving an expandable spinal implant from a collapsed position to an expanded position with less than one full turn of the implant cap and a method for use therewith. A screw lock is disclosed for locking a bone screw to the trailing end of an expandable spinal implant and a method for use therewith.

RELATED APPLICATIONS

This application is a divisional of U.S. application Ser. No.10/094,467, filed Mar. 8, 2002 now U.S. Pat. No. 6,849,093, which claimsthe benefit of U.S. provisional Application No. 60/274,869, filed Mar.9, 2001, the disclosures of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

Expandable implants are known in the field of spinal surgery. Manyexpandable implants require complex mechanisms in order to expand theimplant. Greatly simplifying the expansion of an expandable implant is adevice taught by Michelson in U.S. patent application Ser. No.09/551,964, the disclosure of which is incorporated by reference herein,that moves the implant from a collapsed position to an expanded positionwith less than one full turn of an expander used to expand the implant.Expandable implants often have no provision for preventing theover-expansion of the implant while the implant is being expanded in thedisc space. One of the embodiments of expandable implants taught byMichelson in the '964 application utilizes a hook and peg arrangementthat is integral with the implant to prevent over-expansion.

In certain circumstances, the upper and lower members of the expandableimplant can move away from one another and merely securing the upper andlower members to the adjacent vertebral bodies either with vertebralbody engaging projections or with bone screws is not adequate. Anexample of such a circumstance occurs when the surgeon elects toapproach the spine anteriorly, which generally requires severing, and/orremoving substantial portions of the anterior longitudinal ligament overthe operated area. The anterior longitudinal ligament is positionedalong the anterior spinal surface and prevents hyperextension of thespine as an individual bends backward. Because the anterior longitudinalligament covers the anterior spinal surface, the surgeon must cutthrough this tough ligament to access the disc space below, compromisingthe stability of the spine. Specifically, the anterior longitudinalligament is generally lax, except when an individual leans backward,then the ligament acts as a tension band resisting elongation. If theanterior longitudinal ligament is damaged, there is no check on thatspinal movement and the vertebral bodies may detrimentally angulate.Thus, what is needed is a simple, easy-to-use device that can either orboth expand and prevent the over-expansion of an implant, and furthercan be used, if desired, to lock bone screws to an implant having bonescrews therein.

SUMMARY OF THE INVENTION

The expansion constraining member of the present invention is capable ofone or more of the following functions: (1) expands the implant bymoving the upper and lower members apart, (2) maintains the implant inan expanded state by holding at least a portion of the upper and lowermembers apart so as to maintain the increased height of the implant andresist the collapse of the implant to the collapsed implant height, (3)prevents the implant from expanding beyond a predetermined amount byengaging at least a portion of the upper and lower members, and (4)locks bone screws to the implant by blocking the exit path of the bonescrews in a direction opposite to the direction of insertion. Expansionof the implant preferably increases the implant height only, that is ina plane passing through the mid-longitudinal axis of the implant and theupper and lower members. The expansion constraining member preferablyresists further expansion of the implant and makes possible verticalstability of the implant at its expandable end. The use of screws allowsreconstruction of the function of the anterior longitudinal ligament. Ina preferred embodiment, the expansion constraining member is capable ofperforming all four of the aforementioned enumerated functions.

The expansion constraining member of the present invention offersnumerous advantages over devices of the prior art, a few of whichinclude economy of parts, simplicity, and less mass occupying theinterior of the implant. If the expansion constraining member is also ablocker to maintain the implant in an expandable state, an additionalblocker is not needed in the implant itself. If the expansionconstraining member is also an expander for expanding the implant to anexpanded position, an additional expander is not needed. If theexpansion constraining member is also a lock for locking the bone screwsto the implant, an additional lock to lock the bone screws is notneeded. An expansion constraining member capable of performing theaforementioned functions in one structure reduces the number of partsneeded to perform additional functions. Further, the expansionconstraining member of the present invention is preferably adapted tooccupy less space of the implant interior, thereby increasing theavailable volume for holding fusion promoting materials in the implant.

In accordance with the purposes of the present invention, as embodiedand broadly described herein, an implant cap of this invention isprovided for use in expanding an expandable spinal implant having upperand lower portions adapted to move apart from one another to contactadjacent upper and lower vertebral bodies, respectively, of a humanspine. The cap includes a head having a top surface and a bottom surfaceopposite the top surface. The head is configured to cooperatively engagean end of the implant to at least in part cover an opening in the end ofthe implant. The cap also includes a stem projecting from the bottomsurface of the head. The stem has a distal end, opposed sides having awidth therebetween, and upper and lower surfaces having a heighttherebetween. The width of the stem is greater than the height of thestem proximate the distal end of the stem when the cap is in aninsertion position. The opposed sides are configured to move the upperand lower portions of the implant apart from one another when the cap isrotated from the insertion position to a deployed position.

In accordance with the purposes of a further embodiment of the presentinvention, as embodied and broadly described herein, an implant cap isprovided for use in preventing the over-expansion of an expandablespinal implant having upper and lower portions adapted to move apartfrom one another to contact adjacent upper and lower vertebral bodies,respectively, in the human spine. The cap includes a head configured tocooperatively engage an end of the implant to at least in part cover anopening in the end of the implant. The head has a top surface and abottom surface opposite the top surface. The bottom surface of the headof the cap has either a recess or a protrusion adapted to cooperativelyengage either a protrusion or a recess, respectively, on the end of theimplant to prevent the implant from expanding beyond a predeterminedheight. The cap also includes a stem projecting from the bottom surfaceof the head. The stem is adapted for insertion into the opening of theimplant.

The implant cap may be part of an apparatus for insertion within animplantation space formed across the height of a disc space betweenvertebral bodies of a human spine. The apparatus includes an expandablespinal implant having upper and lower portions adapted to move apartfrom one another to contact adjacent upper and lower vertebral bodies,respectively. The implant has an end having an opening. Each of theupper and lower portions of the implant have either a recess or aprotrusion to cooperatively engage either a protrusion or a recess,respectively, on the bottom surface of the cap to prevent the implantfrom expanding beyond a predetermined height.

In accordance with the purposes of a further embodiment of the presentinvention, as embodied and broadly described herein, a method of thisinvention is provided for engaging an end cap having a stem to anexpandable spinal implant having an end. The method includes the stepsof inserting the stem of the end cap into the end of the implant;rotating the stem of the end cap to expand the height of the implant;and using a portion of the end cap to prevent the implant from expandingbeyond a predetermined height.

In accordance with the purposes of a further embodiment of the presentinvention, as embodied and broadly described herein, a method of thisinvention is provided for expanding an expandable spinal implant havingan end. The method includes the steps of providing an end cap having astem projecting therefrom; inserting at least a portion of the stem ofthe end cap into the end of the implant while the implant is in acollapsed position; and rotating the stem of the end cap less than onefull turn to expand the implant from the collapsed position to anexpanded position.

The accompanying drawings, which are incorporated in and constitute apart of this specification, are by way of example only and notlimitation, and illustrate several embodiments of the invention, whichtogether with the description, serve to explain the principles of theinvention. The scope of the invention is limited only by the scope ofthe claims as from the present teachings other embodiments of thepresent invention shall be apparent to those skilled in the art.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded trailing end perspective view of an expandableinterbody spinal fusion implant with an expanding and constrainingmember in the form of an end cap for expanding the implant, blocking anopening to the implant, restraining over-expansion of the implant, andlocking bone screws to the implant in accordance with a preferredembodiment of the present invention;

FIG. 2 is a leading end perspective view of the end cap of FIG. 1;

FIG. 3A is a trailing end elevation view of the implant of FIG. 1 in acollapsed state;

FIG. 3B is a trailing end elevation view of the implant of FIG. 1 in anexpanded state;

FIG. 4A is a side elevation view in partial cross section of the implantof FIG. 1 in an unexpanded state and with the end cap inserted therein;

FIG. 4B is a fragmentary side elevation view of an expander tool forexpanding an expandable interbody spinal fusion implant from a posteriorapproach to the spine;

FIG. 5 is a side elevation view in partial cross section of the implantof FIG. 1 in an expanded state and with the end cap inserted therein;

FIG. 6 is a trailing end elevation view of the implant of FIG. 1 in anexpanded state with the end cap inserted and in the locked position;

FIG. 7 is a fragmentary cross sectional side elevation view along line7-7 of the implant of FIG. 6 showing a lip portion of the implanttrailing end against the outer perimeter of a recess in the end cap forpreventing over-expansion of the implant;

FIG. 8 is a trailing end perspective view of an expandable interbodyspinal fusion implant with an expanding and constraining end cap forexpanding the implant, blocking an opening to the implant, restrainingover-expansion of the implant, and locking bone screws to the implant inaccordance with another preferred embodiment of the present invention;

FIG. 9 is a trailing end elevation view of the implant of FIG. 8;

FIG. 10 is a side elevation view in partial cross section of the implantof FIG. 8 in an unexpanded state and with the end cap being insertedtherein;

FIG. 11 is a side elevation view in partial cross section of the implantof FIG. 8 in an expanded state with the end cap inserted therein;

FIG. 12 is a trailing end perspective view of an expandable interbodyspinal fusion implant and an end member for constraining over-expansionof the implant in accordance with another preferred embodiment of thepresent invention;

FIG. 13 is a trailing end perspective view of an end member forconstraining over-expansion of the implant in accordance with anotherpreferred embodiment of the present invention;

FIG. 14 is a trailing end perspective view of an expandable interbodyspinal fusion implant with an expansion constraining member in the formof a constraining ring for restraining over-expansion of the implant inaccordance with another preferred embodiment of the present invention;

FIG. 15 is a trailing end elevation view of an expandable interbodyspinal fusion implant in accordance with another preferred embodiment ofthe present invention;

FIG. 16 is a trailing end elevation view of an expansion constrainingmember in the form of a constraining ring for restraining over-expansionof the implant of FIG. 15 in accordance with another preferredembodiment of the present invention; and

FIG. 17 is a side elevation view in partial cross section and hiddenline of the implant of FIG. 15 in an expanded state and with theconstraining ring of FIG. 16 installed.

DETAILED DESCRIPTION OF THE DRAWINGS

Reference will now be made in detail to the present preferredembodiments (exemplary embodiments) of the invention, examples of whichare illustrated in the accompanying drawings.

The expansion constraining member of the present invention is adaptedfor use with expandable interbody spinal fusion implants. To betterunderstand the structure and interrelationship of the expansionconstraining member and the expandable interbody spinal fusion implant,the structure and associated characteristics for one embodiment of animplant adapted to be used with the expansion constraining member of thepresent invention will be described first.

FIGS. 1-7 show a preferred embodiment of an expandable interbody spinalfusion implant 100 and an expansion constraining end cap 200 for usetherewith in accordance with the present invention. The expansionconstraining member of the present invention is not limited for use withimplant 100 and may be used with other expandable interbody spinalfusion implants such as, but not limited to, those taught by Michelsonin WIPO Publication No. 01/56513, entitled “Expandable ImpactedInterbody Spinal Fusion Implant,” U.S. patent application Ser. No.09/612,188, entitled “Expandable Push-In Arcuate Interbody Spinal FusionImplant with Cylindrical Configuration During Insertion,” U.S. patentapplication Ser. No. 09/551,964, entitled “Expandable Threaded ArcuateInterbody Spinal Fusion Implant with Cylindrical Configuration DuringInsertion,” U.S. patent application Ser. No. 09/574,858, entitled“Expandable Threaded Arcuate Interbody Spinal Fusion Implant withLordotic Configuration During Insertion,” U.S. patent application Ser.No. 09/772,309, entitled “Expandable Push-In Arcuate Interbody SpinalFusion Implant with Tapered Configuration During Insertion,” thedisclosures of which are incorporated by reference herein,

As shown in FIGS. 1, 3A, and 3B, implant 100 has a leading end 102, atrailing end 104, an upper member 106, and a lower member 108. Upper andlower members 106, 108 are each preferably arcuate at least in part andadapted for placement toward and at least in part within the upper andlower of two adjacent vertebral bodies, respectively. Upper and lowermembers 106, 108 preferably include at least one opening adapted tocommunicate with one of the adjacent vertebral bodies, the openingsbeing in communication with one another and adapted for permitting forthe growth of bone from adjacent vertebral body to adjacent vertebralbody through the implant. Upper and lower portions 106, 108 alsopreferably define a hollow interior therebetween for holding bone growthpromoting material, the hollow interior preferably being incommunication with the openings in upper and lower portions 106, 108.Trailing end 104 of implant 100 preferably includes openings 122 topermit for the packing of additional fusion promoting substances intothe implant after the implant expansion and the application of thelocking member, and to permit for the growth of bone through implant100.

As shown in FIGS. 4 and 5, upper and lower members 106, 108 are moveablerelative to one another and have a first position that allows for acollapsed implant height and a second position that allows for anincreased height. Upper and lower members 106, 108 are preferablyarticulated at an articulation point proximate leading end 102 ofimplant 100. Upper and lower members 106, 108 are articulated to oneanother at a pivot point 112 so one of the respective ends of upper andlower members 106, 108 remain articulated while the other of therespective ends of upper and lower members 106, 108 are free to moveaway from one another. The cooperating rotational articulation 112preferably is proximate one of the proximal end and the distal end ofupper and lower members 106, 108 at an end opposite to an end cap 200.Other types of articulation as would be known to one of ordinary skillin the art are within the scope of the present invention.

Upper and lower members 106, 108 preferably have an upper screw hole 116and a lower screw hole 118, respectively passing therethrough, eachadapted to receive a bone screw 120 passing from the interior of implant100 into an adjacent vertebral body to anchor implant 100 to an adjacentvertebral body. Bone screws are not essential to the operation of theimplant, but are preferable for providing added securement of theimplant to the adjacent vertebral bodies.

In certain circumstances, upper and lower members 106, 108 can move awayfrom one another and merely securing upper and lower members 106, 108 tothe adjacent vertebral bodies with bone screws is not adequate. Anexample of such a circumstance occurs when the surgeon elects toapproach the spine anteriorly, which generally requires severing and/orremoving substantial portions of the anterior longitudinal ligament overthe operated area. The anterior longitudinal ligament is positionedalong the anterior spinal surface and prevents hyperextension of thespine as an individual bends backward. Because the anterior longitudinalligament covers the anterior spinal surface, the surgeon must cutthrough this tough ligament to access the disc space below, compromisingthe stability of the spine. Specifically, the anterior longitudinalligament is generally lax, except when an individual leans backward,then the ligament acts as a tension band resisting elongation. If theanterior longitudinal ligament is damaged, there is no check on thatspinal movement and the vertebral bodies may detrimentally angulate.Thus, a mechanism is needed to prevent movement of the upper and lowermembers relative to one another beyond a predetermined amount.

The expansion constraining member of the present invention is capable ofone or more of the following functions: (1) expands the implant bymoving the upper and lower members apart, (2) maintains the implant inan expanded state by holding at least a portion of the upper and lowermembers apart so as to maintain the increased height of the implant andresist the collapse of the implant to the collapsed implant height, (3)prevents the implant from expanding beyond a predetermined amount byengaging at least a portion of the upper and lower members, and (4)locks bone screws to the implant by blocking the exit path of the bonescrews in a direction opposite to the direction of insertion. Expansionof the implant preferably increases the implant height only, that is ina plane passing through the mid-longitudinal axis of the implant and theupper and lower members. The expansion constraining member preferablyresists further expansion of the implant and makes possible verticalstability of the implant at its expandable end. The use of screws allowsreconstruction of the function of the anterior longitudinal ligament. Ina preferred embodiment, the expansion constraining member is capable ofperforming all four of the aforementioned enumerated functions.

The expansion constraining member of the present invention offersnumerous advantages over devices of the prior art, a few of whichinclude economy of parts, simplicity, and less mass occupying theinterior of the implant. If the expansion constraining member is also ablocker to maintain the implant in an expandable state, an additionalblocker is not needed in the implant itself. If the expansionconstraining member is also an expander for expanding the implant to anexpanded position, an additional expander is not needed. If theexpansion constraining member is also a lock for locking the bone screwsto the implant, an additional lock to lock the bone screws is notneeded. An expansion constraining member capable of performing theaforementioned functions in one structure reduces the number of partsneeded to perform additional functions. Further, the expansionconstraining member of the present invention is preferably adapted tooccupy less space of the implant interior, thereby increasing theavailable volume for holding fusion promoting materials in the implant.

As shown in FIGS. 1, 3A, and 3B, trailing end 104 also preferably has anopening 124 adapted to engage end cap 200 and may also provide access tothe interior of implant 100 for the purpose of introducing bone growthpromoting materials therein. Upper and lower interior surfaces 126, 128of opening 124 preferably have a portion that extends beyond exteriortrailing end surface 130, forming upper lip portions 132 and lower lipportions 134, respectively. Upper and lower lip portions 132, 134 can bearcs of a circle such that in the expanded state, the arcs would be partof the same circle. For example, when implant 100 is in an unexpandedstate, the profile of upper and lower lip portions 132, 134 preferablyform the shape of at least a portion of an oval as shown in FIG. 3A. Inthe expanded state of implant 100, the profile of upper and lower lipportions 132, 134 preferably becomes less oval and generally morecircular in shape as shown in FIG. 3B.

Cap 200 preferably has a head 202 and a stem 204. Head 202 has aperimeter preferably sized and shaped to cover at least a portion ofupper and lower bone screw holes 116, 118 so as to lock bone screws 120to implant 100. Preferably, the perimeter of head 202 has at least onearcuate portion. Head 202 has a top surface 206, a bottom surface 208,and a rim 210. Top surface 206 has a tool engagement area 212 that ispreferably adapted to cooperatively engage an insertion tool. Toolengagement area 212 preferably includes a hex-shaped recess 214 adaptedto engage the end of a correspondingly-shaped tool. A groove or marking216 allows the surgeon to visually confirm the orientation of end 204when hidden from view. Other shapes are possible for tool engagementarea 212 depending upon the type of insertion tool used with the presentinvention, all of which are within the broad scope of the presentinvention.

Top surface 206 of cap 200 preferably has a bevel 218 extending aroundthe perimeter thereof to form a reduced profile. Top surface 206 mayhave any shape suitable for its intended purpose though it is preferablethat cap 206 generally not extend from trailing end 104 so as to avoidany undesired contact with delicate vascular and/or neurologicalstructures adjacent thereto after implant 100 is installed in the spine.

As shown in FIG. 2, bottom surface 208 of cap 200 has a recess 220proximate the perimeter of bottom surface 208 that is adapted tointeract with upper and lower lip portions 132, 134 of implant 100. Asdescribed in further detail below, the interaction of lip portions 132,143 and recess 120 limits any unwanted expansion or over-expansion ofimplant 100 beyond a predetermined height. Recess 220 has an innerperimeter 222, an outer perimeter 224, and a width therebetween adaptedto accommodate the profiles of at least a portion of upper and lowerlips 132, 134 of implant 100 in both an unexpanded and expanded state.The surface of outer perimeter 224 forms a flange that acts as a stopagainst which upper and lower lip portions 132, 134 of implant 100 areprevented from further movement away from the mid-longitudinal axis ofimplant 100 when implant 100 and cap 200 are engaged, as will bedescribed in more detail below.

Stem 204 of cap 200 projects from bottom surface 208 and is sized andshaped to cooperatively engage opening 124 in trailing end 104 to expandimplant 100 and to maintain implant 100 in an expanded state. Stem 204preferably has a distal end 226 with tabs 228, 230, an upper surface232, a lower surface 234 opposite to upper surface 232, and sides 236,238. Tabs 228, 230 are configured to engage the interior surface oftrailing end 104 such that when properly positioned within opening 124,tabs 228, 230 prevent cap 200 from backing out of opening 124 and lockcap 200 to implant 100.

Sides 236, 238 of stem 204 are configured to cooperatively engage upperand lower interior surfaces 126, 128 of opening 124. Opening 124 mayhave any shape suitable for its intended purpose for interacting withstem 204. For example, sides 236, 238 may be beveled or rounded toaccommodate rotational contact with upper and lower interior surfaces126, 128. Stem 204 may have a generally rectangular cross-section or agenerally circular cross-section along at least a portion of the lengthof the stem. Stem 204 may also have a cross-section with sides 236, 238intersecting the upper and the lower surfaces 232, 234 at junctions,which may be two diametrically opposed corners and two diametricallyopposed arcs. The two diametrically opposed arcs may be each of the sameradius and, preferably, the diagonal or modified hypotenuse between theopposed arcs has a maximum dimension that generally approximates thedistance between the upper and lower surfaces 232, 234 such that whenstem 204 is rotated from a first insertion position toward asecond/deployed position, no substantial over-distraction occurs betweenthe adjacent vertebral bodies as would occur if the height of theimplant were to be increased markedly beyond that obtained in thesecond/deployed position. The two diametrically opposed corners may forma 90-degree angle. Additionally, sides 236, 238 may be configured to bedivergent away from distal end 226 to better accommodate engagement withupper and lower interior surfaces 126, 128 while implant 100 is in theexpanded state.

FIGS. 4-6 show a preferred expansion of implant 100 by cap 200. In FIG.4, stem 204 of cap 200 is inserted through opening 124 in trailing end104 of implant 100. After stem 204 is inserted into opening 124, tabs228, 230 extend beyond upper and lower interior surfaces 126, 128 ofopening 124 and into the interior of implant 100. Upper and lowersurfaces 232, 234 of stem 204 are oriented toward upper and lowerinterior surfaces 126, 128 of opening 124, respectively, such thatimplant 100 is in a collapsed state. As cap 200 is rotated approximately90° in either direction, sides 236, 238 of stem 204 cooperatively engagewith upper and lower interior surfaces 126, 128 of opening 124, forcingapart upper and lower members 106, 108 away from the mid-longitudinalaxis of implant 100 to position implant 100 in an expanded state. Theconfiguration of stem 204 permits implant 100 to be expanded to amaximum implant height with less than one full turn. The rotation of cap200 moves upper and lower members 106, 108 from a generally parallelorientation shown in FIG. 4 to an angled orientation shown in FIG. 5 toexpand or increase the height of implant 100. During expansion ofimplant 100, upper and lower lip portions 132, 134 move within recess220 of cap 200 until stem 204 ceases moving upper and lower interiorsurfaces 126, 128 away from the mid-longitudinal axis of implant 100.Tabs 228, 230 move into cooperative engagement with an interior portionof upper and lower members 106, 108 to lock cap 200 to implant 100 aswell as lock implant 100 in an expanded state. A means to stop rotationof cap 200 when expansion is completed and secured to implant 200 may beemployed. It is also within the broad scope of the present inventionthat cap 200 may be used to expand the implant from a first, collapsedlesser angled orientation to a second, expanded and more angledorientation.

For posterior spinal surgery, cap 200 may be preinstalled at the leadingend of a posterior interbody spinal fusion implant. As shown in FIG. 4B,by way of example and not limitation, an expander tool 800 may be usedto cooperatively engage the stem of cap 200 from an opening in theimplant trailing end. Expander tool 800 has a shaft 802 and a distal end804. Distal end 804 has a pair of prongs 806 and a recess 808therebetween. Prongs 806 and recess 808 cooperate with the stem of cap200 to rotate cap 200 and to move the implant from a collapsed state toan expanded state.

FIG. 7 shows a partial cross-section along line 7-7 of FIG. 6. As shownin FIG. 7, the maximum expansion of upper member 106 is reached whenupper lip portions 132 are blocked from further motion away from themid-longitudinal axis of implant 100 upon reaching outer perimeter 224of recess 220. Although not shown in FIG. 7, lower lip portions 134similarly contact outer perimeter 224 of recess 220. In this manner,expansion of implant 100 beyond a predetermined amount is prevented.Tabs 228, 230 of stem 204 bear against the interior of implant 100 andprevent removal of end cap 200 from opening 124. In the deployedposition, end cap 200 locks implant 100 in an expanded state, and isitself secured from inadvertent dislodgement.

As shown in FIGS. 8-11, another preferred embodiment of the implant andend cap of the present invention is shown and generally referred to bythe reference numbers 300 and 400, respectively. Implant 300 is similarto implant 100, except that opening 324 of implant trailing end 304preferably has at least one thread 336 for cooperatively engaging with athreaded stem 404 of cap 400.

Cap 400 is similar to cap 200, except for differences noted below. Head402 has a perimeter including an upper cutout portion 440 and a lowercutout portion 442, each being adapted to allow the passage of a bonescrew 320 into implant 300 after cap 400 has been attached to implant300. Once bone screws 320 are inserted, cap 200 may be rotated such thatat least a portion of head 402 covers each of screws 320. Upper andlower cutout portions 440, 442 allow the surgeon the option of insertingbone screws 320 before or after attachment of cap 400 with implant 300.

Stem 404 has at least one thread 448 along the mid-longitudinal axis ofcap 400 for cooperatively engaging with threaded opening 324 of implant300. Distal end 426 of stem 404 has an upper surface 444 and a lowersurface 446 that are at least in part tapered or convergent towardsdistal end 426 for assisting in the insertion of stem 404 into opening324 of implant 300.

As shown in FIGS. 10 and 11, cap 400 is inserted into trailing end 304of implant 300, preferably by aligning the edge of distal end 426 withthe plane separating upper and lower members 306, 308. Once upper andlower surfaces 444, 446 of distal end 426 are sufficiently withinthreaded opening 324 of implant trailing end 304, cap 400 is rotated toallow stem thread 448 of cap 400 to cooperatively engage with threadedopening 324. The engagement of stem thread 448 with threaded opening 324spreads apart upper and lower members 306, 308 at least along a portionof the length of implant 300. Continued rotation of cap 400 forces upperand lower lip portions 332, 334 to contact recess 420 of cap 400. Thepitch of thread 448 is preferably such that as upper and lower lipportions 332, 334 reach recess 420, they come into contact with at leasta portion of the outer perimeter of recess 420. Upon contact with recess420, upper and lower lip portions 332, 334 are prevented from furthermovement away from the mid-longitudinal axis of implant 300. Cap 400makes possible the full insertion of the bone screws either before orafter the implant is expanded.

Those skilled in the art will appreciate that although it is preferredto use a cap to prevent over-expansion of an expandable implant, theinvention is not so limited. For example, the implant trailing end maybe adapted to have lip portions along the trailing end interior surfacefor cooperatively engaging with a recess and/or flange to preventover-expansion of the implant. In such an instance, an over-expansioninhibiting surface may operate without a stem and/or head by relying onadditional surface features of the implant trailing end, for example, akey-way entry along the opening leading to the interior lip portions ora circumferential barrier beyond the interior lip portions forpreventing the over-expansion surface from traveling too far into theimplant interior. It should also be apparent to those skilled in the artthat the expander implant cap of the present invention may be adaptedfor use with a wide variety of expandable spinal implants, for exampleonly, threaded cylindrical or frustoconical implants and impacted,push-in implants of various cross sectional shapes.

In other preferred embodiments, the expansion constraining member of thepresent invention need not be in the form of a cap. For example, FIGS.12 and 13 show other preferred embodiments of expansion constrainingmember for constraining expansion of an implant 500. Implant 500 hasupper and lower screw holes 516, 518 adapted to receive screws 520 tosecure an expansion constraining member 600 to implant 500.

Expansion constraining member 600 preferably has a bar 602 and twoopenings 604. Screw openings 604 have an inner surface 606 adapted toaccommodate screws 520 to lock expansion constraining member 600 toimplant 500. Inner surface 606 may be threaded or smooth. Those ofordinary skill in the art will appreciate that bar 602 may be of anyshape suitable for the intended purpose of restraining theover-expansion of implant 500.

Bar 602 may be planar or non-planar depending upon the orientation ofthe central axis of each of upper and lower screw holes 516, 518 inrelation to the plane of upper and lower members 506, 508. For example,bar 602 may be non-planar to accommodate implant 500 in an expandedstate while aligning screw holes 604 with upper and lower screw holes516, 518 of implant 500 when upper and lower screw holes 516, 518 eachhave a central axis generally parallel to the plane of upper and lowermembers 506, 508, respectively. Further, upper and lower screw openings516, 518 of implant 500 may have a central axis that is angled withrespect to the plane of each of upper and lower members 506, 508 ofimplant 500 so that screws 520 may assist in anchoring implant 500, aswith screws 120 and implant 100.

After implant 500 is moved to its second, expanded state the surgeonpositions bar 602 at trailing end 504 of implant 500 and aligns screwholes 604 with each of upper and lower screw holes 516, 518. Screws 520are inserted to lock bar 602 to implant 500.

In FIG. 13, another preferred embodiment of the expansion constrainingmember of the present invention is shown and generally referred to bythe reference number 700. Expansion constraining member 700 is similarto expansion constraining member 600 except it has a peg 708 extendingtherefrom instead of a screw. A screw is passed through screw hole 704to secure bar 702 to an implant.

FIG. 14 shows an implant 900 and expansion constraining member in theform of a ring 1000. Implant 900 is similar to implant 500 except thatopening 924 has upper and lower lip portions 932, 934. Lip portions 932,934 differ from those described in relation to implants 100 and 300 inthat upper lip portion 932 has a thread 938 on the interior surfacethereof, and lower lip portion 934 has a thread 940 on the interiorsurface thereof. Threads 938, 940 are adapted to mate with a thread 1006of constraining ring 1000, described below.

Constraining ring 1000 has an inner surface 1002 and an outer surface1004. Outer surface 1004 has thread 1006 adapted to mate with threads938, 940 of implant 900. Inner surface 1002 has a tool engagement area1008 adapted to cooperatively engage a tool for attaching constrainingring 1000 to implant 900. Constraining ring 1000 may be adapted to lockbone screws to implant 900 in a similar fashion as described in relationto implants 100 and 300.

Implant 900 may be expanded to its second, expanded state. Thereafterconstraining ring 1000 may be inserted into opening 924 of implant 900and screwed around the inner perimeter of upper and lower lip portions932, 934. While these later embodiments are shown in relationship to thetrailing end of the implant without bone screws that has been done forsimplicity and these and other means can be adapted to serve the purposeof locking the bone screws.

FIGS. 15-17 show an implant 1100 and expansion constraining member inthe form of a ring 1200. Implant 1100 is similar to implant 900 exceptthat lip portions 1132, 1134 differ from those described in relation toimplant 900 in that upper lip portion 1132 and lower lip portion 1134have a thread portion 1138, 1140 respectively, on the exterior surfacethereof. Implant 1100 also has upper and lower screw holes 1116, 1118that are adapted to receive bone screws 1120 in a similar fashion asdescribed in relation to implants 100 and 300.

Constraining ring 1200 is similar to constraining ring 1000 except thatinner surface 1202 has thread 1206 adapted to mate with threads 1138,1140 of implant 1100. Outer surface 1204 may have a tool engagement areaadapted to cooperatively engage a tool for attaching constraining ring1200 to implant 1100.

Implant 1100 may be expanded to its second, expanded state. Thereafter,constraining ring 1200 is attached to implant 1100 by screwing ring 1200around the outer perimeter of upper and lower lip portions 1132, 1134 tolock bone screws 1120 to implant 1100 and constrain the over-expansionof implant 1100 as shown in FIG. 17.

The expandable spinal implant and expander implant cap may be made ofartificial or naturally occurring material suitable for implantation inthe human spine. The implant and/or cap may comprise at least in partbone, metal including, but not limited to, titanium and its alloys,surgical grade plastics, plastic composites, ceramics, or any othermaterial suitable for the intended purpose. The material may bebioresorbable.

The expandable spinal implant and/or cap of the present invention may becoated with, treated with, comprised of, be used in combination with, orhave a hollow for containing bone growth promoting materials and/orsubstances, including but not limited to, bone, bone derived products,demineralized bone matrix, ossifying proteins, bone morphogeneticproteins, hydroxyapatite, and genes coding for the production of bone.The spinal implant and/or cap of the present invention can be formed ofa material that intrinsically participates in the growth of bone fromone of adjacent vertebral bodies to the other of adjacent vertebralbodies, can be a source of osteogenesis, or can be at least in partbioabsorbable or resorbable. The implant and/or cap of the presentinvention can be formed of a porous material.

At least one of the implant and cap of the present invention may bemodified, or used in combination with materials to make it antimicrobialor antibacterial, such as, but not limited to, electroplating or plasmaspraying with silver ions or other substance. The expandable spinalimplant and/or cap of the present invention may be coated with,comprised of, be used in combination with, or have a hollow forcontaining one or more chemical substances and/or compounds adapted toinhibit scar formation.

While various embodiments of the present invention are presented by wayof example only and not limitation, common to each of them, is that theexpandable spinal implant for insertion across the disc space betweentwo adjacent vertebral bodies of a human spine has surface featuresadapted to cooperatively engage with a recess of an attachable piece forinhibiting over-expansion of the implant.

There is disclosed in the above description and the drawings caps, alock, expansion constraining members, expanders, and implants, whichfully and effectively accomplish the objectives of this invention.However, it will be apparent that variations and modifications of thedisclosed embodiments may be made without departing from the principlesor the scope of the present invention.

1. An apparatus for insertion within an implantation space formed acrossthe height of a disc space between vertebral bodies of a human spine,said apparatus comprising: an expandable spinal implant having upper andlower portions adapted to move apart from one another to contactadjacent upper and lower vertebral bodies, respectively, said implanthaving an end having an opening, each of said upper and lower portionshaving a recess; and an implant end cap having a head configured tocooperatively engage said end of said implant to at least in part coversaid opening, said head having a top surface and a bottom surfaceopposite said top surface, said bottom surface having at least oneprotrusion adapted to cooperatively engage said recesses of said upperand lower portions of said implant to prevent said implant fromexpanding beyond a predetermined height by limiting movement of saidupper and lower portions relative to one another, said implant end capbeing rotated to engage said at least one protrusion and said recesses.2. The apparatus of claim 1, wherein said head is configured tocooperatively engage said end of said implant to completely cover saidopening.
 3. The apparatus of claim 1, wherein said implant has aplurality of bone screw holes, said bottom surface of said head beingconfigured to cover at least a portion of one of said bone screw holeswhen said cap is engaged to said implant.
 4. The apparatus of claim 3,wherein said bottom surface of said head is configured to cover aportion of more than one of said bone screw holes when said cap isengaged to said implant.
 5. The apparatus of claim 3, wherein said headis configured to allow the insertion of a bone screw into said implantafter said cap is engaged with said implant.
 6. The apparatus of claim3, wherein said head has a perimeter that is configured to permit theinsertion of a bone screw into one of said bone screw holes after saidcap is engaged with said implant, said head being movable to cover atleast a portion of the bone screw after the bone screw is inserted inone of said bone screw holes.
 7. The apparatus of claim 1, wherein saidupper and lower portions of said implant include at least one openingadapted to communicate with one of the adjacent vertebral bodies, saidopenings in said upper and lower portions being in communication withone another and adapted for permitting for the growth of bone fromadjacent vertebral body to adjacent vertebral body through said implant.8. The apparatus of claim 7, wherein said implant includes a hollowinterior for holding bone growth promoting material, said hollowinterior being in communication with at least one openings in each ofsaid upper and lower portions.
 9. The apparatus of claim 1, wherein saidimplant is in combination with a bone growth promoting material.
 10. Theapparatus of claim 9, wherein said bone growth promoting material isselected from one of bone, bone derived products, demineralized bonematrix, ossifying proteins, bone morphogenetic protein, hydroxyapatite,and genes coding for the production of bone.
 11. The apparatus of claim1, wherein said implant is treated with a bone growth promotingsubstance.
 12. The apparatus of claim 1, wherein said implant comprisesat least one of the following materials: metal, titanium, plastic, andceramic appropriate for implantation in the human body.
 13. Theapparatus of claim 1, wherein said implant is at least in partresorbable.
 14. The apparatus of claim 1, wherein said implant is formedof a porous material.
 15. The apparatus of claim 1, wherein said implantis in combination with a material adapted to inhibit scar formation. 16.The apparatus of claim 1, wherein said implant is in combination with anantimicrobial material.
 17. An apparatus for insertion within animplantation space formed across the height of a disc space betweenvertebral bodies of a human spine, said apparatus comprising: anexpandable spinal implant having upper and lower portions adapted tomove apart from one another to contact adjacent upper and lowervertebral bodies, respectively, said implant having an end having anopening, each of said upper and lower portions having at least oneprotrusion; and an implant end cap having a head configured tocooperatively engage said end of said implant to at least in part coversaid opening, said head having a top surface and a bottom surfaceopposite said top surface, said bottom surface having a recess adaptedto cooperatively receive said protrusions of said upper and lowerportions of said implant to prevent said implant from expanding beyond apredetermined height by limiting movement of said upper and lowerportions relative to one another, said implant end cap being rotated tofacilitate receipt of said protrusions in said recess.
 18. The apparatusof claim 17, wherein said head is configured to cooperatively engagesaid end of said implant to completely cover said opening.
 19. Theapparatus of claim 17, wherein said implant has a plurality of bonescrew holes, said bottom surface of said head being configured to coverat least a portion of one of said bone screw holes when said cap isengaged to said implant.
 20. The apparatus of claim 19, wherein saidbottom surface of said head is configured to cover a portion of morethan one of said bone screw holes when said cap is engaged to saidimplant.
 21. The apparatus of claim 19, wherein said head is configuredto allow the insertion of a bone screw into said implant after said capis engaged with said implant.
 22. The apparatus of claim 19, whereinsaid head has a perimeter that configured to permit the insertion of abone screw into one of said bone screw holes after said cap is engagedwith said implant, said head being movable to cover at least a portionof the bone screw after the bone screw is inserted in one of said bonescrew holes.
 23. The apparatus of claim 17, wherein said upper and lowerportions of said implant include at least one opening adapted tocommunicate with one of the adjacent vertebral bodies, said openings insaid upper and lower portions being in communication with one anotherand adapted for permitting for the growth of bone from adjacentvertebral body to adjacent vertebral body through said implant.
 24. Theapparatus of claim 23, wherein said implant includes a hollow interiorfor holding bone growth promoting material, said hollow interior beingin communication with at least one openings in each of said upper andlower portions.
 25. The apparatus of claim 17, wherein said implant isin combination with a bone growth promoting material.
 26. The apparatusof claim 25, wherein said bone growth promoting material is selectedfrom one of bone, bone derived products, demineralized bone matrix,ossifying proteins, bone morphogenetic protein, hydroxyapatite, andgenes coding for the production of bone.
 27. The apparatus of claim 17,wherein said implant is treated with a bone growth promoting substance.28. The apparatus of claim 17, wherein said implant comprises at leastone of the following materials: metal, titanium, plastic, and ceramicappropriate for implantation in the human body.
 29. The apparatus ofclaim 17, wherein said implant is at least in part resorbable.
 30. Theapparatus of claim 17, wherein said implant is formed of a porousmaterial.
 31. The apparatus of claim 17, wherein said implant is incombination with a material adapted to inhibit scar formation.
 32. Theapparatus of claim 17, wherein said implant is in combination with anantimicrobial material.
 33. A method for expanding an expandable spinalimplant having an end, the method comprising the steps of: providing anend cap having a stem projecting therefrom; inserting at least a portionof the stem of the end cap into the end of the implant while the implantis in a collapsed position; and rotating the stem of the end cap lessthan one full turn to expand the implant from the collapsed position toan expanded position.
 34. The method of claim 33, wherein the step ofrotating the stem includes rotating the stem approximately 90 degrees.35. The method of claim 33, wherein the step of rotating the stemincludes rotating a stem having no threads.
 36. The method of claim 33,further comprising the step of locking the cap to the implant.
 37. Themethod of claim 33, further comprising the step of locking the implantin an expanded position.
 38. The method of claim 33, wherein the implanthas a plurality of bone screw holes, further comprising the step ofcovering at least a portion of the bone screw holes with at least aportion of the end cap.
 39. The method of claim 33, further comprisingthe step of inserting at least one bone screw in the implant after thestem of the end cap is inserted into the end of the implant.
 40. Themethod of claim 33, wherein the end of the implant includes an openingleading to an interior hollow having a bone growth promoting materialtherein, further comprising the step of covering at least a portion ofthe opening with the end cap.
 41. The method of claim 33, wherein thestep of inserting includes inserting a non-threaded stem into the end ofthe implant.
 42. An apparatus for insertion within an implantation spaceformed across the height of a disc space between vertebral bodies of ahuman spine, said apparatus comprising: an expandable spinal implanthaving upper and lower portions adapted to move apart from one anotherto contact adjacent upper and lower vertebral bodies, respectively, saidimplant having an end having an opening, each of said upper and lowerportions having a recess, said implant having a plurality of bone screwholes; and an implant end cap having a head configured to cooperativelyengage said end of said implant to at least in part cover said opening,said head having a top surface and a bottom surface opposite said topsurface, said bottom surface having at least one protrusion adapted tocooperatively engage said recesses of said upper and lower portions ofsaid implant to prevent said implant from expanding beyond apredetermined height by limiting movement of said upper and lowerportions relative to one another, said bottom surface of said head beingconfigured to cover at least a portion of one of said bone screw holeswhen said cap is engaged to said implant.
 43. An apparatus for insertionwithin an implantation space formed across the height of a disc spacebetween vertebral bodies of a human spine, said apparatus comprising: anexpandable spinal implant having upper and lower portions adapted tomove apart from one another to contact adjacent upper and lowervertebral bodies, respectively, said implant having an end having anopening, each of said upper and lower portions having at least oneprotrusion, said implant having a plurality of bone screw holes; and animplant end can having a head configured to cooperatively engage saidend of said implant to at least part cover said opening, said headhaving a top surface and a bottom surface opposite said top surface,said bottom surface having a recess adapted to cooperatively receivesaid protrusions of said upper and lower portions of said implant toprevent said implant from expanding beyond a predetermined height bylimiting movement of said upper and lower portions relative to oneanother, said bottom surface of said head being configured to cover atleast a portion of one of said bone screw holes when said cap is engagedto said implant.